Comparison of Aspergillus niger spore production on Potato Dextrose Agar (PDA) and crushed corncob medium.

Minimizing the number of generations through which a culture passes from the initial culture until its recovery at the fi nal stage of fermentation is a general principle. For fi lamentous fungi, a large number of generations can cause the appearance of low-yield producing variants and mutant strains, which are generally genetically unstable. The use of successive sub-cultures can decrease the degree of relationship, causing a decrease in productivity. In order to reduce problems with strain deterioration, all cultures maintained as stock-cultures must be prepared from only one spore of the parental strain. From stock-culture, the microorganism is inoculated in tubes containing agar solidifi ed in an inclined position, resulting in a fi rst-generation culture. For preparation of working-inocule, spores of the fi rst-generation are suspended in a Tween solution and used to inoculate Petri plates containing agar. The inoculation must be carried out over the total agar surface; otherwise growth will be irregular and a uniform culture will not be obtained. Spores produced in the plates are then recovered in Tween solution and used for inoculations of working-media (McNeil and Harvey, 1990). Several articles have applied agarized medium as an inoculum to Aspergillus niger (Ates et al., 2006; Dinu et al., 2007; Djekrif-Dakhmouche et al., 2006; ElEnshasy et al., 2006; Mlakar and Legiša, 2006). The disadvantages in applying agar medium are low spore production and diffi culties in obtaining spores, such as defi xing of agar from plates during mechanical shaking and the loss of material when transferring the suspension to another recipient. Solid-state fermentation allows the production of aerial conidia of biological control fungic agents (Ye et al., 2006). Semi-solid media has been developed and tested in strains of different genera, such as Beauveria, Trichoderma and Metarhizium, and this technology was considered more appropriate to large-scale production of fungic spores (Cavalcante et al., 2008; Kang et al., 2005; Prakash et al., 2008; Roussos et al., 1991). Semi-solid culture media are predominantly used in Brazil in large-scale production of entomopathogenic fungi, such as Metarhizium anisopliae, which was traditionally done using cooked rice as the substrate (Faria and Magalhães, 2001; Loureiro et al., 2004). Bianchi et al. (2001) have studied the production of J. Gen. Appl. Microbiol., 56, 399‒402 (2010)